1. Field of the Invention
The present invention relates to a method for detecting the position of a moving body and, in particular, to a method for detecting the position of a moving body in which the position of a moving body can be detected with a high degree of accuracy.
2. Description of the Related Art
Conventional methods for detecting the position of a moving body are the method used in GPS (Global Positioning Systems) and those used in PHS (Personal Handy phone Systems) and the like.
In the method used in GPS, the distance (i.e. the pseudo range) between GPS satellites and a moving body is calculated using the radio wave propagation time between the GPS satellites and the moving body. Respective spheres that take the calculated pseudo range between the moving body and each of four GPS satellites as the radiuses thereof are determined, and the intersect point of these spheres is used as the position of the moving body.
In the method used in PHS, the fact that the area from which a signal can be received of a base station capable of receiving radio waves transmitted from a PHS terminal is limited is used effectively, and the position of the person holding the PHS terminal is detected from the position of the base station receiving the radio waves from the PHS terminal.
However, among the above conventional moving body position detecting methods, in the method used in GPS, the drawback exists that, if it is not possible to pick up four or more GPS satellites simultaneously, then it is not possible to detect the position of the moving body. In the method used in PHS, although it is possible to pinpoint the position of the holder of the PHS terminal as being within the area covered by the base station (within 100 to 300 meters), the drawback exists that it is difficult to detect this position with a high degree of accuracy.
Therefore, an object of the present invention is to provide a method for detecting the position of a moving body in which the position of the moving body can be detected with a high degree of accuracy.
In order to achieve the above object, the present invention provides a moving body position detection method for detecting a current position of a mobile station (for example, the vehicle 1 in the embodiment) capable of movement and also capable of data communication between itself and at least fixed stations (for example, the radio base stations 3 in the embodiment) using radio waves, wherein precise positions of the fixed stations are stored in advance in the mobile station, clocks (for example, the radio wave clocks 10 in the embodiment) are provided for keeping a common time respectively in the fixed stations and the fixed stations send radio waves containing time information of the clocks, the mobile station receives the radio waves sent by the fixed stations and calculates distances between the mobile station and the fixed stations by determining differences between a clock (for example, the clock 15 in the embodiment) provided in the mobile station and the time information contained in the radio waves, and the mobile station calculates the position of the mobile station from the calculated distances and from the precise positions of the fixed stations that were stored in advance. By employing this type of structure, it is possible to determine the precise position of the mobile station by calculating the distances between the mobile station and three or more fixed stations. Accordingly, even in a location where conventional GPS satellites cannot be used, it is still possible to accurately determine the position of the mobile station.
Furthermore, in the present invention, it is also possible for the position of the mobile station to be calculated using a combination of information from the fixed station and information from GPS satellites (for example, the GPS satellites 8 in the embodiment). By employing this type of structure, it is possible to calculate the position of the mobile station even when it is not possible to calculate the position of the mobile station using the fixed stations alone or GPS satellites alone. Therefore, it is possible to find the position of the mobile station more accurately than when a conventional method is used.
Furthermore, in the present invention, it is preferable if the mobile station performs communication with the fixed stations using the same transmission method as is used in the GPS satellites.
Furthermore, in the present invention, it is also possible for the clocks in the fixed stations to be set based on time information from the GPS satellites (8). By employing this type of structure, it is possible to obtain accurate time information from the GPS satellites that are provided with atomic clocks. Therefore, for example, accurate time is guaranteed even when it is not possible to receive radio waves from a radio wave clock.
Furthermore, in the present invention, it is also possible for the clocks in the fixed stations to be set based on time information sent by a radio wave clock base station (12) as well as on the positions of the fixed stations and the radio wave clock base station.
Furthermore, in the present invention, it is also possible, when information cannot be obtained from a predetermined number of fixed stations, for the mobile station to calculate the position of the mobile station by substituting information from the GPS satellites for the information that should have been obtained from the fixed stations.